RF coils of various design are available for use in MR imaging. The coils are used to receive/transmit signal and in order to do this should be positioned directly on or immediately adjacent the human anatomy in an orientation so that the coil lies in a plane which is parallel to the axis of the bore of the magnet.
The coils include a top portion and a bottom portion. In regard to coils for imaging the head, these are generally channel shaped and facing one another so as to envelope the head with side edges which are close or touching so that the head is surrounded by the two coil portions. Each coil portion includes an array of coil elements, typically four, so as to form a phased coil array.
Such coils can be provided as rigid coils or as flexible foam coils. The rigid coils have a specific geometrical shape that can not be changed and are also usually designated for certain anatomy such as the head or chest where they are designed with the required shape to approximate to the average patient.
Flexible coils are known and commercially available. These can be conformed to patient anatomy, but have to be held in place by using external fixation method such as straps with suitable fastening arrangements. That is the flexible coils typically can be bent into the required shape to match the anatomy, but have no ability to remain in that shape due to their elastic nature. Thus they must be fastened into place to maintain the required shape and position.
MR imaging is carried out often in a diagnostic situation where the patient is conscious and not sterile so that the coil can be attached into place by such straps. Thus flexible coils are typically or commonly used in this situation since the fastening is not a problem.
In another field of use, MR imaging is carried out in an intra-operative situation where the patient is unconscious and draped to maintain sterility. In this case, due to difficulty of cleaning or sterilizing the straps, the use of flexible coils in intra-operative applications is limited. Thus, up to now, typically rigid coils have been used in this situation with the coils mounted rigidly from a suitable support such as the bed frame or a head fixation device. Coils, whether rigid or flexible, that are used for neurosurgical applications generally have rigid attachment to the patient table or directly to the patient, which makes the mechanical/geometrical adjustment of the coil difficult or impossible.
Such rigid coils can be sterilized as required. However they provide only a compromise in relation to the position of the coil antenna relative to the anatomy of the patient. As is well known, improved images are obtained where the antenna is located in the best position relative to the anatomy concerned and best orientation relative to the magnetic field. Thus the best images are obtained with the closest proximity combined with an orientation which is closest to parallel to the longitudinal axis of the bore, as opposed to being at an angle to the longitudinal axis. As rigid coils are necessarily sized to fit all, in many cases they do not properly fit the patient. Also the mounting typically is restrictive as to the ability to properly orient the coil